1. Field of the Invention
The present invention relates to a lens barrel configured to collapse a lens group in one mode and to use the lens group advanced to a predetermined position in another mode.
2. Description of the Related Art
Imaging apparatuses such as digital still cameras and digital video cameras (hereinafter, collectively referred to as the “digital camera”) are facing strong demands for improvements in imaging performance and portability. To meet these demands, some imaging apparatuses are configured to, when shooting, extend lens groups in a photographing optical system from a camera easing while positioning the lens groups at distances necessary for the shooting from an image pickup device, and when not shooting, to retract at least one of the lens groups from a photographic optical axis and to collapse the lens groups in the camera casing with the distances between the lens groups and the image pickup device minimized to be less than a minimum distance required for shooting. Such an imaging apparatus has a smaller dimension in the photographic optical axis direction (hereinafter also referred to as a thickness dimension) when a lens barrel is in a collapsed state with a movable lens barrel stored, and is therefore suitable for carrying.
However, in the above technique, the retracted position of the lens groups retracted from the photographic optical axis is actually inside of the maximum outside diameter of a fixed cylinder portion of a camera main body. Therefore, while the thickness dimension when the movable lens barrel is stored can be reduced, the outside diameter of the fixed cylinder portion is increased. This leads to a problem that the camera main body (imaging apparatus) is increased in size when viewed from the front (object side).
To counter this problem, there has already been known a lens barrel configured to retract at least one of the retractable lens groups with a retractable lens retaining frame which retracts the lens group to the outside of the inside diameter of the fixed cylinder portion (Japanese Patent Application Publication No. 2006-330657). In the lens barrel, a retracting frame drive mechanism having a retracting frame drive source different from a back-and-forth drive source for moving the movable lens barrel in the photographic optical axis direction retracts the retractable lens retaining frame to the outside of the fixed cylinder portion in the process of collapsing when the lens group is collapsed (when no photographing is performed). As compared to the conventional configuration to retract the lens groups to the inside of the fixed cylinder portion, this lens barrel can neither cause an increase in the outside diameter of the movable lens barrel nor cause increases in the distances between the lens groups in the collapsed state.
However, the conventional lens barrel described above still has room for improvement in terms of miniaturization, since the retracting frame drive source for the retracting frame drive mechanism is provided in addition to the back-and-forth drive source.